A conventional converter device of this kind comprises a two capacitors connected in series as the smoothing capacitors due to the convenience of a rated voltage, one of which is connected with a load to become for instance a control power source. FIG. 2 is a circuit diagram showing the converter device in which reference numeral (1) designates a converter comprising for instance diodes for converting three phase AC power supplied from a commercial power source into a DC power, numerals (2a 2b) designate smoothing capacitors connected in series and provided at the DC output side of the converter (1), numeral (3) designates a first load being fed with the DC power by using the smoothing capacitors (2a), (2b) as the DC power source, numeral 4 designates a load connected in parallel with the smoothing capacitor (2b) to become for instance a control power source for a control circuit (not shown). Although the voltage of the two terminals P-N of the smoothing capacitors (2a, 2b) connected in series is 400V, the load (4) is fed with the voltage lower than 400V between the two terminals Q-N of the smoothing capacitor (2b).
However, if one of the two smoothing capacitors connected in series is connected to the load (4) to supply with a current Io thereto, the voltage between the terminals Q-N of the smoothing capacitor (2b) connected to the load (4) comes down, then the voltage between the terminals P-Q of the other smoothing capacitor (2a) comes up so much, thereby causing a voltage unbalance. The thus raised voltage becomes higher than the rated voltage of the smoothing capacitor (2a) to possibly damage the smoothing capacitor. Therefore the smoothing capacitors (2a, 2b) are connected respectively in parallel with dummy resistors (5a, 5b).
In the conventional converter device as stated above, the dummy resistors (5a, 5b) are constantly connected in parallel with the smoothing capacitors (2a, 2b) so that the currents I.sub.1, I.sub.2 flow through the dummy resitors (5a, 5b) thereby causing the power consummed by the dummy resistors to increase its loss.